The total quantity of stone that was sunk within the cones, and on the intermediate dike, from the year 1784 to the end of December 1790, being seven years, amounted to 373,359 cubic toises, or about 5,900,000 tons.
These 18 cones being sunk at irregular distances from each other, some being 25 toises, and others at 800 toises from centre to centre, occupied a line of 1950 toises in length. The distance of the first cone from the Island Pelee, on the east, was 510, and of the eifhteenth to Fort Querqueville on the west 1200 tones; so that the whole entrance or opening of the roadstead of Cherbourg was original ly 8660 toises, more than one-half of which was now imperfectly covered by the breakwater.
The expence of this great undertaking was not, we suspect, accurately known, and could not, proba bly, be ascertained. M. de Cessart estimates the eighteen cones alone, at 6,231,407 lines, or about L. l60,000; and the total expence incurred between the 1st April 1788 and the 1st January 1791, he states as under Making the general total 21,658,420 0 0 or L.900,000 Sterling. In this estimate the extra pay to the troops and seamen employed, would not appear to be included ; for M. de. Curt, in his re port to the National Assembly, states the total ex pence to have amounted to 32,000,000 Byres, or L. 1,300,000 Sterling; and that a farther sum would be required of 879,648 Byres, to bring the top of the dike to an uniform height, namely, a little above the level of the surface, at low water, of ordinary tides.
The number of people employed was prodigious. To enable M. de Cessart to complete and sink five cones a-year, he found it necessary to. employ 250 carpenters, SO blacksmiths, 200 stone-hewers, and 200 masons,—in all 680 artificers. The number of quarrymen, and others, employed in transporting 174,720.cubic toises of stone for the 64 cones ori ginally intended, or 13,650 yearly, was estimated at 400 workmen, 100 horses, 30 drivers, 24 c.hasses marees, each carrying seven cubic takes, or about 98 tons, with 100 seamen ; making an aggregate, for this service, of 526 men, and for the whole operation from 1200 to 1500 artificers and labourers, to which were actually superadded about 3000 soldiers.
A very considerable part of the expence might have been saved by dispensing altogether with the cones, all of which burst, as might have been ex the superincumbent weight of a deep co of water, pressing the stones within against their sides. The 9th cone, which was sunk in 1786,
went to pieces in 1800, after standing fourteen years; another reached the duration of five years; six re mained on an average about four years ; and all the rest went in pieces within a year from the time of their being sunk.
The failure of the cones, and the breaking out of the Revolution, put an entire stop, for some time, to all operations at Cherbourg. The attention, how ever, of the National Assembly was speedily called to what they considered to be an object of great na tional importance. In 1791 they directed their Committee for the Marine to make out a detailed report of the operations that had already been car ried on. On this report being given in by M. do Curt, in the name of the Committee, it was read and approved by the Assembly, and funds to a certain extent decreed, to complete the undertaking on a new plan proposed by M. de Cessart. The principal feature of this plan was that of casing over the sur face of the dike as it then stood with large blocks of stone ; and to carry the height of the breakwater along the whole of its extent, so far above the high water mark of spring-tides, as to reader it capable of receiving batteries on the summit, at the middle, and at the two extremities.
The slope of the side next to the road Lead was found on examination to sustain itself unaltered at an angle of 45 degrees, but the slope on the side next to the sea, whose base was three for one of height, had given way to the depth of fourteen feet below the low water mark and the materials being composed of small stones, were washed away, and had formed themselves into a prolonged slope of one foot only in height for ten feet of base, which was therefore concluded to be the natural slope made by the sea when acting upon a shingly shore ; a conclusion, however, too vague to be correct, as the slope occasioned by the action of the sea must de pend on the nature of the materials against which it acts, and the force and direction of the acting power. A sandy beach, for instance, has invariably the most gradual slope, gravel the next, shingles the next, and large masses of rock or stone, the most pre cipitous. At the present time, the stones of the breakwater, by constant friction, have worn away the sharp angles, and it has been found that the • base on the side next to the sea is on the average fully eleven for one of perpendicular height.